A bolder grille treatment highlights the exterior changes on the range-topping , but the bigger news is what's behind the radiator of this pillarless hardtop: two new direct-injected bi-turbo V-8s—a 429-bhp 4.7-liter unit in the CL550 and a 5.5-liter version in the CL63 AMG.

In addition to the boost in horsepower, both engines have more torque—the CL550 produces 516 lb.-ft., which helps it accelerate to 60 mph in a claimed 4.8 seconds. The AMG powerplant comes in two states of tune—with 536 bhp and 590 lb.-ft. of torque in base form, or with 563 bhp and 664 lb.-ft. of torque when equipped with the optional performance package. The 0 to 60 mph times are 4.4 and 4.3 seconds, respectively.

The CL63 AMG's combination of multi-clutch 7-speed sequential-shift transmission with the fuel-saving engine stop/start system lacks the refinement of the CL550 4Matic, which has a more traditional 7-speed automatic with a torque converter.

Stop/start, which functions only when the car is in Eco mode, cuts the engine when the car is stationary and automatically restarts it when the accelerator is pressed. The combination of the clutched gearbox and the slight delay in restarting the engine can catch you out. In the hybrid version of the with stop/start, there's much quicker response thanks to the electric motor assist.

Putting the transmission into sport or manual mode deactivates the AMG's stop/start system. The CL550, on the other hand, feels much more of a piece thanks to its linear power delivery and the smooth-shifting gearbox. When the Controlled Efficiency driving mode is selected on the CL550, its fuel-saving strategy starts the car out in 2nd gear and will upshift quickly to keep the revs down, engaging 6th gear at speeds as low as 37 mph.

Both models offer a host of driver's aids, including a lane-departure and blind-spot warning system that now incorporates a braking function designed to keep the car in its lane. Again, this may be a case of being overly ambitious with technology. One can appreciate the warnings—a subtle tug on the steering wheel to warn about lane departure and the visual telltale in the mirrors are appreciated—but it's a little unsettling to feel the brakes come on automatically as a way to keep the car in its lane of travel. Fortunately, there is a way to deactivate the automatic braking.

One slick piece of technology is the new split screen that allows the passenger to watch videos on the center screen, while the driver's view is limited to the standard set of navigation, radio and control screens.

Also returning to the lineup are two V-12 models, the 510-bhp CL600 and 621-bhp CL65 AMG. Pricing starts at $114,025 for the CL550, $151,125 for the CL63 AMG, $157,000 for the CL600 and $210,175 for the CL65 AMG.